The present invention relates to a method for operating a transmission amplifier, such as a communications terminal, with the transmission amplifier being fed with a supply voltage, and with any nonlinearity of the transmission amplifier being substantially compensated for via a predistortion unit for data values in an input data stream, and to an apparatus for operating the transmission amplifier.
A transmission spectrum of a communications terminal, such as a mobile telephone, has to satisfy relevant requirements which are included in Standards that have to be complied with. These include the fact that the output power of the transmission spectrum in adjacent radio channels must not exceed limit values which can be found in the Standards. As such, depending on the respective type of modulation which is used by the communications terminal and which may, for example, be QPSK for (W)CDMA, it is necessary to use a transmission amplifier for the communications terminal whose linearity is subject to very stringent demands.
Transmission amplifiers such as these are costly and have a rather low energy efficiency.
For this reason, lower-cost transmission amplifiers are widely used, particularly for mobile radio base stations, and are driven well into the nonlinear region of their characteristic, which leads to high power efficiency. The pronounced nonlinearity which occurs as a consequence is compensated for by a linearization technique, wherein the incoming raw digital data is modified via a digital predistortion unit such that, overall, the actually desired linear gain is produced at an output of the transmission amplifier.
The predistortion unit thus compensates for the nonlinearity of the transmission amplifier and, if necessary, of further electronic components which influence the data values via suitable predistortion values for the digital data values.
Against this background, the present invention is directed toward providing a method and an apparatus which allow energy-efficient transmission amplifiers, which themselves satisfy stringent requirements for their linearization, to be used in communications terminals.